In the related art, a device that detects an obstacle present in front of a vehicle from output of a radar mounted on the vehicle and predicts collision between the detected obstacle and the host vehicle is known. However, when the vehicle travels on a descending slope, a subjacent object present on a front side of the descending slope is detected as an obstacle, similar to a collision target on a flat road. Here, the subjacent object refers to an iron plate, an iron rail or the like provided on a road surface, which is an obstacle with no likelihood of collision with the host vehicle. Further, the collision target refers to a stopped vehicle or the like on a road, which is an obstacle with a likelihood of collision with the host vehicle.
In this regard, Patent Literature 1 discloses a collision prediction device that is provided with slope determination means for determining whether a host vehicle is traveling on a slope. Here, if the slope determination means determines that the host vehicle is traveling on the slope, the collision prediction device reduces collision determination sensitivity.